1. Field of the Invention
The present invention relates to initially colorless chromogenic, color precursor compounds having particular utility in the field of carbonless copying. The compounds of the present invention may be utilized, for example, in the production of self-marking impact papers of the transfer or manifolding type wherein a first marking ingredient is carried on one sheet of paper for reaction with a second marking ingredient normally carried on a mating sheet of paper. More particularly, the invention relates to a family of chromogenic oxime ether of Michler's hydrol color precursor compounds having the following structural formula: ##STR3## wherein R.sub.1 and R.sub.2 each represents an organic radical. More preferably, R.sub.1 should represent either a lower alkyl group having from 1 to 5 carbon atoms or a phenyl group and wherein R.sub.2 should represent a substituted or unsubstituted phenyl group having the following formula: ##STR4## wherein R.sub.3 and R.sub.4 each separately represents either a hydrogen atom, a chlorine atom or a nitro group.
2. Description of the Prior Art
Impact or pressure sensitive carbonless transfer papers have recently come into wide usage in the United States and throughout the world. Ordinarily, such papers are printed and collated into manifolded sets capable of producing multiple copies. In this connection, pressure applied to the top sheet causes a corresponding mark on each of the other sheets of the manifolded set.
The top sheet of paper, upon which the impact or pressure is immediately applied, ordinarily has its back surface coated with microscopic capsules containing one of the reactive ingredients which produces a mark. A receiver sheet placed in contact with such back face of the top sheet has its front surface coated with a material having a component reactive with the contents of the capsules so that when capsules are ruptured upon impact by stylus or machine key, the initially colorless or substantially colorless contents of the ruptured capsules spill out to react with a coreactant therefor on the receiver sheet and a mark forms on the receiver sheet corresponding to the mark impressed by the stylus or machine key.
In the art, impact transfer papers are designated by the terms CB, CFB and CF, which stand respectively for "coated back", "coated front and back" and "coated front". Thus, the CB sheet is usually the top sheet and the one on which the impact impression is directly made; the CFB sheets are the intermediate sheets, each of which have a mark formed on the front surface thereof and each of which also transmits the contents of ruptured capsules from its back surface to the front of the next succeeding sheet; and the CF sheet is the last sheet and is only coated on its front surface to have an image formed thereon. The CF sheet is not normally coated on its back surface as no further transfer is desired.
While it is customary to coat the capsules on the back surface and to coat the co-reactant for the capsules contents on the front surface of each sheet, this procedure could be reversed if desired. Further, with some systems, coatings need not be used at all and the co-reactive ingredients may be carried in the sheets themselves, or one may be carried in one of the sheets and the other may be carried as a surface coating. Further, the reactants may both comprise microencapsulated liquids. Patents illustrative of many of the various kinds of systems which may incorporate such co-reactive ingredients and which may be used in the production of manifolded transfer papers include, for example, U.S. Pat. Nos. 2,299,694 to Green, 2,712,507 to Green, 3,016,308 to Macaulay, 3,429,827 to Ruus and 3,720,534 to Macaulay et al.
The most common variety of carbonless impact transfer paper, and the type with which the compounds of the present invention are preferably utilized, as the type illustrated, for example, by Green (2,712,507) and Macaulay (3,016,308) wherein microscopic capsules containing a liquid fill comprising a solution of an initially colorless chemically reactive color forming dye precursor are coated on the back surface of the sheet, and a dry coating of a co-reactant chemical for the dye precursor is coated on the front surface of a receiving sheet.
Many color precursors useful in connection with carbonless copying systems are known to those skilled in the art to which the present invention pertains. For example, specific reference is made to the color precursors mentioned in the patent to Phillips, Jr. et al, U.S. Pat. No. 3,455,721 and particularly to those listed in the paragraph bridging columns 5 and 6 thereof. Other color precursors are disclosed in 3,703,397 and 3,713,863 to Lin et al. These color precursor materials are capable of reacting with a CF coating containing an acidic material such as the acid-leached bentonite-type clay disclosed in British Pat. No. 1,381,928, the entirety of which is hereby specifically incorporated by reference, or the acid-reactant organic polymeric material disclosed in the Phillips, Jr. et al 3,455,721 patent. Additional disclosures of acidic coatings which are capable of converting the color precursors into their highly colored form are set forth in U.S. Pat. Nos. 3,622,364, 3,330,722, 3,389,007 and 3,293,060.
The color precursors disclosed in the patents listed above are initially generally colorless and capable of undergoing an acid-base type reaction to become highly colored when brought into contact with an acidic layer such as an acid-leached bentonite-type clay or an acid-reacting polymeric material, or the like. Other previously known color precursors are the spiro-dipyran compounds disclosed in the patent to Harbort, U.S. Pat. No. 3,293,060 with specific reference being made to the disclosure of the 3,293,060 patent extending from column 11, line 32 through column 12, line 21.
Generally speaking, the color precursor materials disclosed above are dissolved in a solvent and the solution is encapsulated in accordance with the procedures and processes described and disclosed by Macaulay (3,016,308) and by Green (3,712,507) as mentioned above. Other processes for encapsulating color precursors are disclosed in U.S. Pat. No. 3,429,827 to Ruus and U.S. Pat. No. 3,578,605 to Baxter. In this connection, it should be mentioned that the exact nature of the capsule itself is not critical as long as the same is capable of containing the color precursor and can be ruptured by the application of pressure in accordance with conventional carbonless copying procedures. Solvents known to be useful in connection with dissolving color precursors include chlorinated biphenyls, vegetable oils (castor oil, coconut oil, cotton seed oil, etc.), esters (dibutyl adipate, dibutyl phthalate, butyl benzyl adipate, benzyl octyl adipate, tricresyl phosphate, trioctyl phosphate, etc.), petroleum derivatives (petroleum spirits, kerosene, mineral oils, etc.), aromatic solvents (benzene, toluene, etc.), silicone oils, or combinations of the foregoing. Particularly useful are the alkylated naphthalene solvents disclosed in U.S. Pat. No. 3,805,463 to Konishi et al.
In the color forming systems outlined above, as will be appreciated by those skilled in the art, the color precursors are conventionally contained in pressure rupturable microcapsules which are included in the back coatings of the sheets of carbonless copying manifolded sets. Further, it will be appreciated that the acidic coatings are generally utilized as front coatings with the color precursor material in a solvent therefor being transferred from an adjacent back coating to the acidic layer front coating upon rupture of the capsules which contain the color precursor material.